The basic process of installing buried pipelines generally includes the steps of digging a long trench for the pipeline, laying out sections of pipe end to end and adjacent to the trench line, joining the sections of pipe into a continuous pipeline, placing the pipeline into the trench, backfilling the trench, and hydro-testing the pipeline, prior to putting the pipeline into service.
The pipeline must be held off the ground during the pipeline assembly process, the joining together of the individual sections of pipe, and upon installation of the pipeline in the trench.
During the pipeline joining process, the sections of pipe are generally supported off the ground to prevent pipe and coating damage as well as to provide full and easy access to each pipe joint for joining.
The most prevalent method of supporting pipes outside the trench prior to joining is the use of large wooden skids, which are positioned in an alternating, interlocking box pattern that can be scaled to whatever height is required. This method may be rather costly, since the skids which are relatively heavy, must be manually placed prior to lowering of the pipe sections and later manually removed and loaded onto trucks following the placement of the pipeline into the trench. Mechanical removal methods are also available but can be costly as well.
U.S. Pat. No. 7,278,613 to Roy is directed to a pipeline skid and a skid system for use in pipeline construction.
Support cones made of polymeric material are also sometimes used for supporting pipe sections out of trench, but typically only for small diameter pipes of less than 24 inches diameter (600 mm diameter or less). These cones have a pipe size and weight limitation and are meant for a single height and are not used in the trench. These cones are not usable for supporting the pipeline in the trench, since they are typically too tall and do not have sufficient load bearing capacity to support the pipeline during backfilling and continuity testing during which the pipeline is completely filled with water. Of course, the water used for hydrostatic testing adds a significant amount of weight to be supported, in fact a multiple of the weight of the pipeline itself. The cones are particularly prone to collapse when sideways forces are applied under load, because of twisting, bending, or sideways movement of the pipeline during the installation process.
Installations of buried pipelines in areas where rocks or stones are present often require some form of protection to prevent damage to the coating of the pipes, or the pipe itself. For proper pipeline installation, the pipeline must be held off the bottom of the trench to allow for the free flow of backfill material in the trench and around the pipeline. Current methods for holding the pipe up off the trench bottom are expensive and can cause pipeline damage.
In trench pipeline support is currently achieved in various ways. The in trench supporting methods used are intended to not only prevent damage to the pipe but also to prevent interference with the pipe corrosion protection methods used. Generally, pipeline corrosion is prevented by injecting a low voltage protection current of one volt into the soil, which current is transmitted to the pipe and prevents corrosion at locations where the pipe coating may have been damaged, thereby exposing the metal of the pipe to the soil. Electrical contact between the pipe and the soil is generally made through water in the soil.
US 2003/0218103 is directed to a pipeline support for in trench pipeline support.
One in trench support method includes the placement of piles of sand in the trench to hold the pipeline off the trench bottom until backfilling. Although this can be a suitable method for light, small diameter pipelines (up to 323.9 mm diameter), it is often unsuitable for larger diameter pipelines, since the uneven support provided by a sand pile may cause the pipe to deform and become oval which is an unacceptable and expensive problem to remedy. Moreover, the installation of sand piles is very difficult in installations wherein the pipeline is joined above the trench, since it is hard to reach over the pipe to properly place the sand piles in the trench.
Another in trench supporting method employs sandbags, which are installed in the trench to hold the pipeline off the trench bottom. If not properly placed, sandbag supports can create a hard spot where the pipeline is likely to dent or oval, which is an unacceptable and expensive problem to remedy, as mentioned above. More importantly, the sheer number of sandbags required with this method, all of which have to be manually placed, makes it very difficult to ensure proper care is maintained in the sandbag placement. Finally, since sandbags must be positioned manually, safety is a concern with personnel in the pipeline trench for extended periods, since trench depth often exceeds 4 feet (1.2 m) and trenches may be subject to ground water intrusion.
Foam can be sprayed into the trench to hold the pipeline off the trench bottom until back filling. This pipeline supporting method may raise concerns over the environmental impact of the foaming chemical. Moreover, cost of the foam materials is relatively high, the foam requires significant time to harden to the point where it can support the weight of the pipeline and there is a definite potential for the cured strength of the foam being insufficient for supporting the pipeline during continuity testing. Finally, the availability of and access to foaming equipment is an issue, particularly in remote areas and in rugged terrain. Of course, the foam material also has the potential to shield the pipeline's cathodic protection system.
The use of foam pillows placed into the pipeline trench to hold the pipeline off the trench bottom until back filling is also known. The foam pillows used are generally pre-fabricated and are typically covered in plastic to somewhat address the potential concerns over the environmental impact of the foam material. However, as with the sandbag method, the placement of the foam pillows often requires personnel in the trench. In addition, foam pillows are lightweight and can either be blown or floated out of position prior to the pipeline being installed (ground water is often present in areas of stony or rocky terrain). Another significant concern with using foam pillows is the high likelihood of cathodic shielding. As mentioned above, the electrical system of protecting the pipeline steel from rusting by injecting a low voltage current into the ground is impeded by the foam and/or plastic covering and the material of the foam pillows themselves.
Consequently a method and apparatus for supporting a pipeline or pipe sections prior to installation (out of trench) and/or once installed (in the trench) is required which overcomes at least one of the problems encountered with current pipeline supporting methods and apparatus.